Method and device for the design of two parameter distribution system

ABSTRACT

A device and method especially suited for use in the design of a cable television signal distribution system includes a chart having mutually perpendicular axes representing the signal intensities at the Channels 2 and 13 picture carrier frequencies respectively. Modules representing individual components of the distribution system are each dimensioned to correspond to the loss of signal strength at each of the two reference frequencies on passage of a signal through the corresponding component. Each module is positioned on the chart with one of its corners at a point on the chart corresponding to the input signal strengths for the particular component. The signal strengths at the output of that component can then be read from the chart by reference to the position of a second corner of the module on the chart. By the use of L-shaped modules to represent a signal-dividing component and by positioning an outer corner between the legs of the module at a point on the chart corresponding to the input signal strengths for the particular component, an inner corner between the legs of the module is then positioned on the chart at a point corresponding to the signal strengths at the through-line output of the component while the legs of the module have such lengths that the signal strengths at a branch or tap output of the component can be read from the chart scales for the point of intersection of projections of the end edges of the legs of the module.

United States Patent 1 Cappon 1 Jan. 2, 1973 [54] METHOD AND DEVICE FORTHE DESIGN OF TWO PARAMETER DISTRIBUTION SYSTEM Inventor: John Cappon, 1Cathcart Street,

Willowdale, Ontario, Canada Filed: June 28, 1971 Appl. No.: 157,288

References Cited UNITED STATES PATENTS 9/1918 Morichard ..116/130 2/1941Jakosky 10/1965 Prince 7/1969 Amlinger ..33/l SD PrimaryExaminer-Richard B. Wilkinson Assistant Examiner-Stanley A. WalAttorney.l. Noel Walton [57] I ABSTRACT A device and method especiallysuited for use in the designof a cable television signal distributionsystem includes a chart having mutually perpendicular axes representingthe signal intensities at the Channels 2 and 13 picture carrierfrequencies respectively. Modules representing individual components ofthe distribution system are each dimensioned to correspond to the lossof signal strength at each of the two reference frequencies on passageof a signal through the corresponding component. Each module ispositioned on the chart with one of its comers at a point on the chartcorresponding to-the input signal strengths for the particularcomponent. The signal strengths at the output of that component can thenbe read from the chart by reference to the position of a second cornerof the module on the chart. By the use of L-shaped modules to representa signal-dividing component and by positioning an outer corner betweenthe legs of the module at a point on the chart corresponding to theinput signal strengths for the particular component, an inner cornerbetween the legs of the module is then positioned on the chart at apoint corresponding to the signal strengths at the through-line outputof the component while the legs of the module have such lengths that thesignal strengths at a branch or tap output of the component can be readfrom the chart scales for the point of intersection of projections ofthe end edges of the legs of the module.

26 Claims, 7 Drawing Figures Q .59 CHANNEL 13p in dBmV(211.25 MHz) @53as Ol -67- U 30 25 20 i 50 A v 5:1 35 7O Z Q LO 7; D g 73 5 F E} 30- 5 a[E 68 l 'D E 25--- 5' (it A u l l PATENTEDM 2am 3.708.653

sum 3 OF 4 97 103 Ch. 13 (dBmV) 105 95' M/N.2-200 M/N.2l00

Ch.13 (dBmV) w 705 0 1.0 30 0 10 0 PS I x 3 E U l- 10 m U I INVENTOR: 0John Cappon METHOD AND DEVICE FOR THE DESIGN OF TWO PARAMETERDISTRIBUTION SYSTEM BACKGROUND OF THE INVENTION The present inventionrelates to a method and devices for determining the values of twovariable parameters at any desired location within a distribution systemthroughout which system the parameters have varying values. Moreparticularly, this invention relates to a method and devices of theaforesaid type and which method and devices are particularly useful inthe design of a cable television signal distribution system.

With the continuously increasing adoption of cable television signaldistribution systems, there is a correspondingly growing need for amethod and device which will facilitate the design of such a systemthereby to reduce the considerable time presently involved incalculating the signal strengths at various locations throughout such asystem so as to ensure that each and every subscriber to the systemreceives the best possible service while reducing to the greatestpossible extent the numberof relatively expensive system components suchas in-line amplifiers which are required.

Although there has in recent years been increasing use of computers forcarrying out the relevant design calculations, such use of computers is,of course, relatively expensive and the preparation of the necessaryprogrammes and input data for a computer requires considerable time andeffort, with the concomitant risk of human error. Additionally, such useofa computer in such design calculations is undesirable in that iteliminates the potential for compromise which is possible when designdecisions are made on a human basis.

It is accordingly a principal object of this invention to provide amethod and device of the aforesaid type which method and device areespecially applicable to use in the design of a cable television signaldistribution system.

Other objects of the invention will become apparent as the descriptionherein proceeds.

SUMVMARYYOF THE INVENTION The present invention involves the use ofmodules representing the various components of a distribution system.Such a module can then be disposed on a chart yet to be described sothat changes in the parameter values which occur between an input and anoutput of a corresponding component of the system can then readily bedetermined by reference to the chart.

Although the invention is particularly applicable to use in the designofa cable television signal distribution system, it is equallyapplicable to other distribution systems in which two parameters havevalues which vary throughout the system. The invention will, however, bedescribed in detail herein with reference to its use in the design ofcable television signal distribution systems.

Broadly, the method of this invention for determining the values of twovariable parameters at a desired location within a distribution systemthroughout which said parameters have varying values comprises the stepsof disposing on a chart having mutually angularly oriented first andsecond scales respectively representing values of said two parameters amodule representing a preselected portion of said distribution systemand having a first dimension corresponding to the change in the value ofone of said two parameters between input and output points of saidpreselected portion of said distribution system and a second dimensioncorresponding to the change in the value of the other of said twoparameters between said input and output points of said preselectedportion of said distribution system, said first and second dimensions ofsaid module being coterminous at first ends thereof at a referenceposition and being mutually angularly oriented in correspondence withthe mutual angular orientation of said first and second scales of saidchart and said module being disposed on said chart with said referenceposition thereof at a position on said chart corresponding to the valuesof said two parameters at said input point of said preselected portionof said distribution system and with said first and second dimensions ofsaid module disposed parallel to respective ones of said first andsecond scales of said chart; identifying a read-out position on saidchart corresponding to an outer end of a resultant of said first andsecond dimensions of said module; and reading from said first and secondscales of said chart values of respective ones of said two parameterscorresponding to said outer end of said resultant of said first andsecond dimensions of said module, thereby to give the values of said twoparameters at said output point of said preselected portion of saiddistribution system.

As already indicated, the present invention also provides a device foruse in carrying out the method of the invention. Such a device canbroadly be defined as comprising a chart having recorded thereonmutually angularly oriented first and second scales respectivelyrepresenting values of the two parameters, and a module representing apreselected portion of the distribution system and having a firstdimension corresponding to the change in value of one of said twoparameters between input and output points of said preselected portionof said distribution system and a second dimension corresponding to thechange in value of the other of said two parameters between said inputpoint and said output point of said preselected portion of saiddistribution system, said first and second dimensions of said modulebeing coterminous at first ends thereof at a reference position andbeing mutually angularly oriented in correspondence with the mutualangular orientation of said first and second scales of said chart,whereby, when said module is disposed on said chart with said referenceposition of said module at a position on said chart corresponding to thevalues of said two parameters at said input point of said preselectedportion of said distribution system and with said first and seconddimensions of said module disposed parallel to respective ones of saidfirst and second scales of said chart, a read-out position can beidentified on said chart by locating the outer end of a resultant ofsaid first and second dimensions of said module in turn to allow valuesof respective ones of said two parameters to be read from respectiveones of saidf rst and second scales of said chart, the resultingreadings being indicative of the values of respective ones of said twoparameters at said output point of said preselected portion of saiddistribution system.

In accordance with another feature of this invention, there is provideda module for use in designing a radio frequency signal cabledistribution system, which module can broadly be defined as including agenerally planar undersurface and a top surface and which module hasindicia visibly recorded thereon to designate a correspondingsignal-modifying component of a radio frequency signal cabledistribution system, said module having mutually angularly orientedfirst and second side edges coterminous at a first corner of saidmodule, said first side edge of said module having at least a sectionthereof with a length corresponding to the change in signal intensity ata first frequency on passage of a radio frequency signal through the corresponding component between an input and an output thereof, said secondside edge of said module having at least a section thereof with a lengthcorresponding to the change in signal intensity at a second frequency onpassage of a radio frequency signal through the corresponding componentbetween the input and the output thereof, and said module having asecond corner disposed at an outer end of a resultant of said sectionsof said first and second side edges of said module.

Other particular features of the invention as well as the advantagesresulting from its utilization will become apparent as the descriptionherein proceeds.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be describedmerely by way of illustration with reference to the accompanyingdrawings in which:

FIG. 1 is a schematic diagram of part of a cable television signaldistribution system showing a trunk line of that system as well asfragmentarily showing two distribution line sections extending from thetrunk line;

FIG. 2 is a fragmentary plan view of one embodiment of a device inaccordance with the present invention and showing modules of the devicedisposed on a chart, the particular modules shown representing thevarious components of part of one of the distribution line sections ofthe system shown in FIG. 1;

FIG. 3 is an enlarged perspective view of one of the modules shown inFIG. 2; I

FIG. 4 is a plan view similar to that of FIG. 2 but illustrating the useof aparticularly preferred type of module, the several modulesrepresenting the various componentsof part of a second one of thedistribution line sections of the system shown in FIG. 1;

FIG. 5 is an enlarged perspective view of one of the modules shown inFIG. 4;

FIG. 6 shows an alternative type of chart for use in the method of thisinvention and having representations of further relevant parametervalues provided thereon; and

FIG. 7 illustrates a device in accordance with the invention andincluding an overlay as an optional additional feature which may beprovided.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Before describing theembodiments of the method, device and modules in accordance with thisinvention as illustrated in FIGS. 2 to 7 of the accompanying drawings,that part of a cable television signal distribution system shown in FIG.1 will first be described and the manner in which the invention isapplied to the design of that system will then be explained.

The cable television distribution system shown in FIG. 1 includes atrunk distribution line generally indicated at 10 and extending from acable television head-end which will frequently include communityantenna television signal-receiving equipment. Two bridger-amplifiersgenerally indicated at 11 and 12 are shown as being provided in aconventional manner in the trunk line 10 and distribution line sectionsgenerally indicated at 14 and 15 are shown as extending from thebridger-amplifiers 11 and 12 respectively. Other distribution lines ordistribution line sections (not shown) will in practice be connected tothe trunk line 10 at spaced apart locations therealong as isconventional. Further amplifiers, such as the bridger-amplifiers l1 and12, will be provided, as required, along the trunk line 10 so as toensure that adequate signal is provided to each and every suchadditional distribution line or distribution line section connectedthereto.

The distribution line section 14 shown in FIG. 1 includes a first cable18 having a length of 200 feet and extends from the output of thebridger-amplifier 11 to a conventional three-way splitter 19 havingthree outputs indicated at 20, 21 and 22. The separate distributionlines connected to the splitter outputs 20 and 22 are shownfragmentarily and will not be described further herein. The distributionline extending from the splitter output 21 is shown in FIG. 1 asincluding five two-way tap-offs 24, 25, 26, 27 and 28. The two tapoutputs of each of these tap-offs are utilized to provide service toindividual subscribers served by the system and are accordingly locatedat appropriate positions along the distribution line section 14. It willparticularly be noted from FIG. 1 that a cable 29 extends from theoutput 21 of the splitter 19 to the input of the tap-off 24 while cables30, 31, 32 and 33 serially interconnect the tap-offs 24, 25,26, 27 and28. A further cable 34 is shown frag mentarily as extending from theoutput of the tap-off 28. Further tap-offs can, of course, be providedin the cable 34. It will also be noted from FIG. 1 that theaforementioned cables have the following lengths:

Cables 18 and 29 The several tap-offs in the distribution line section14 and their operating characteristics will be considered in furtherdetail hereinafter.

The distribution line section 15 includes a directional coupler 36connected to the bridger-amplifier 12 by a cable 35 having a length of200 feet. The through line output of the directional coupler 36 is shownas being connected to a cable 37 which extends to one or more furtherdistribution or feeder lines (not shown). The branch output 38 of thedirectional coupler 36 is shown in FIG. 1 as being connected to adistribution line including five tap-offs 39, 40, 41, 42 and 43. It willbe seen that tapoff 42 has two tap outputs while the remaining tap-offsare four-way ones. Accordingly, each of those remaining tap-offs hasfour tap outputs. It will also be noted that a cable 44 having a lengthof 150 feet connects the branch output 38 of the directional coupler 36to the input of the tap-off 39 while cables 45, 46, 47 and 48, eachhaving a length of feet, serially interconnect the individual tap-offs39, 40, 41, 42 and 43. A l00-foot cable 49 extends from the throughoutput of the tap-off 43 to a distribution line amplifier 50.

During their passage through the various cables and components, such asdirectional couplers, splitters and tap-offs, constituting thedistribution system, the signals being distributed therethrough will, asis well known, suffer progressive attenuation and it is for this reasonthat amplifiers, such as amplifiers 11, 12 and 50, are provided atappropriate positions throughout the system. The extent to whichamplifiers need to be provided in a distribution system such as thatshown in FIG. 1 depends of course to a very considerable extent on thedisposition, number and characteristics of the components such assplitters, directional couplers and tap-offs in the system. Otherfactors yet to be considered are, however, also significant. It willfurther be understood that components such as directional couplers,splitters and tap-offs are utilized whenever it is required to divide asignal between two or more lines of the system. Accordingly, suchcomponents will be identified generally herein as signal-dividingcomponents" or signal dividers.

The design of a cable distribution system such as the system shown inFIG. 1 of the accompanying drawings involves the careful selection ofcomponents such as directional couplers, splitters and tap-offs so as toensure that each subscriber receives satisfactory signal strength whilerequiring the use in the system of a minimum number of amplifiers andother relatively expensive system components. In designing such adistribution system, the designer has a wide range of components withdifferent operating characteristics available'to him and he must selectfrom such available components those which will provide the desiredperformance in the most effective, efficient and economic manner. Forexample, directional couplers, splitters and tap-offs giving differentdistributions of an input signal between the several output lines ofsuch a component are availablesFor example, a designer mustalso payattention to the fact that, if he selects a directional coupler whichprovides a'greater signal strength to a branch line extending from thatcoupler, then less signal strength will remain for the through line andadditional amplifiers might well then need to beprovided in the throughline. Alternatively, by using a signal divider, such as a directionalcoupler, which provides less signal strength to its branch output, fewersubscribers can then be served from the distribution line connected tothe branch output unless one or more distribution line-amplifiers areconnected in that distribution line. The signal strength which isrequired in a distribution line will, of course, in turn depend on manyfactors of which there may be mentioned the length of that line, thenumber of tap-offs connected in that line, andthe minimum and maximumacceptable signal strength levels to be made available to eachsubscriber served by that line. Theminimum and maximum signal strengthlevels required at a tap output of any tap-off in a distribution linewill also be determined by reference to the-length of drop-line orlead-in cable which will be connected to that tap output.

It should also be understood that'the changes in signal intensity whichoccur on passage through some of the components ofa distribution system,such as that shown in FIG.-l,will be different at different frequencies.For this reason, it is customary, when designing such a system, tocalculate the signal strengths and losses for two different signalfrequencies. In contemporary cable television systems, such calculationsare usually made for frequencies of 55.25 MHz and 21 1.25 MHz, thesebeing the frequencies of the picture carrier signals for existingtelevision Channels 2 and I3 respectively.

As already explained, it has heretofore been conventional to selectcomponents such as splitters, directional couplers and tap-offs for usein cable television signal distribution systems by lengthy calculationson the basis of the known operating characteristics of the availablecomponents. Regardless of whether such calculations are made manually orby means of a computer, they require considerable time to complete andconsequently increase the design cost and the risk of error.Furthermore, computer calculation often precludes compromise and isoften somewhat lengthy since the computer will often consider designpossibilities which will be eliminated in manual design as beingobviously impractical.

The manner in which the present invention facilitates the design ofadistribution system such as that shown in FIG. 1 while still allowingthe benefits ofpersonal judgment to be obtained will now be explainedfirst with reference to FIGS. 2 and 3 of the accompanying drawings,which figures show a particularly simple embodiment of a device inaccordance with the present invention. As previously indicated, FIG. 2refers solely to one part of the distribution line section I4 of thesystem shown in FIG. 1. More particularly, FIG. 2 refers to that part ofthe distribution line section 14 which extends from the output of thebridger-amplifier 11 to the through output of the tap-off 28. Thesignals from the outputs 20 and 22 of the splitter 19 are not, however,represented in FIG. 2. Merely by way of illustration, it can beindicated that the splitter 19 is considered to be one which provides asignal strength attenuation of 3.5 db between its input and its output21 at each of the aforementioned reference frequencies of 55.25 MHz and211.25 MHz.

The device in accordance with the invention and generally indicated atin FIG. 2 of the drawings includes a chart 61 which is optionallysecured to a backing board 62 by thumb tacks 63. The chart 61 hasprinted on its upper surface first and second logarithmic Cartesianscales 64 and 65. The ordinate scale 65 represents the signal intensityin dBmV at the aforementioned Channel 2 picture carrier frequency of55.25 MHz while the abscissa scale64 represents the signal intensity ofthe Channel 13 picture carrier frequency of 211.25 MHz in the sameunits. The signal strength level at any point on the chart 61 can thenbe reported as the Cartesian co-ordinates (x, y) of that point where 1:represents the Channel 13 picture signal intensity in dBmV and yrepresents the Channel 2 picture signal intensity in dBmV. It should,however, be appreciated that it is not essential that the twoaxes haveidentical scales. This invention involves the disposition on the chart61 of modules representing the various components of the portion of theactual distribution system being designed so that the signal strengthlevels at the two specified frequencies at any position in the systemcan be read-for corresponding points on the chart 61. The manner inwhich this is done will be explained in more detail hereinafter. Beforesuch an explanation is given, it should, however, be noted that, tofacilitate understanding of the invention, the signal strength levels atvarious positions throughout the system illustrated are numericallyindicated in FIG. 1 in the form of the aforementioned (x, y)co-ordinates.

Referring now in greater detail to the device 60 shown in FIG. 2, itwill be -foot that it includes a plurality of modules A through L whichare freely positionable as required on the chart 61. Each of theaforementioned modules A through L represents a given signal-modifyingcomponent of the distribution line section 14. To facilitateunderstanding further, the module legends are shown parentheticallyagainst the corresponding component legends on FIG. 1. In particular, itwill be seen that the module A represents the ZOO-foot length of cable18 extending from the branch output of the bridger-amplifier 11 to theinput of the splitter 19. The module B represents the losses in signalstrength which occur between the input of the splitter 19 and the outlet21 thereof. The modules D, F, H, .l and L represent respective ones ofthe tap-offs 24, 25, 26, 27 and 28. The module C represents the 200-footcable 29 between the output 21 of the splitter 19 and the I input of thetap-off 24 while the module E represents the l50f-foot cable 30 betweenthe through output of the tap-off 24 and the input of the tap-off 25.Similarly, the modules G and K represent the ISO-foot lengths of cablebetween the tap-offs'25, 26 and 27, 28 respectively while the module 1represents the l75-foot cable 32 between the tap-offs 26 and 27. Theactual signal strength values referred to herein with reference to thedrawings are based on the use of foamed dielectric, aluminum sheath linecable having an outside diameter of 0.412 inch. The invention is not, ofcourse, restricted in any way to the use of that particular size ofcable.

Referring now to FIG. 3, it will be seen that the module C shown thereinand representing the 200-foot cable 29 between the output of thesplitter 19 and the input of the tap-off 24 has a generally rectangularconfiguration with first and second sides or dimensions 70 and 71 whichare coterminous at a first corner or reference position 72 ofthe module.The length of the first side 70 of the module C corresponds to the lossof signal strength at the Channel 13 picture carrier frequency of 211.25MHz as a signal passes through the 200-foot cable 29, the dimensionalscale being the same as that of the abscissa 64 of the chart 61.Similarly, the length of the second side 71 of the module C correspondsto the loss of signal strength through the ZOO-foot cable 29 at theChannel 2 picture carrier frequency of 55.25 MHz. It will now beunderstood that, if the module C is placed on the chart 61 with its side70 parallel to the Channel [3 axis 64, with its side 71 parallel to theChannel '2 axis 65 and with its first corner 72 at a position on thechart 61 corresponding to the Channels 2 and 13 signal strengths at theinput end of the cable section 29 (i.e. the signal strengths at theoutput 21 of the splitter 19), the signal strengths for the twofrequencies at the second or other end of the cable section 29, i.e. atthe tap-off 24, can then be read from the chart 61. In particular, itwill be understood that the corner 73 of the rectangular module Cdiagonally opposite to the first corner 72 thereof will then be disposedon the chart 61 at a position corresponding to the signal strengths atthe second end of the cable section 29. Adopting the terminology ofvector analysis, the corner 73 can be defined as being disposed at theouter end of the resultant of the sides and 71 of the module C. Similarconsiderations apply to all the modules A through L.

Assuming that it is known that the signal strength level at the branchoutputs of each of the bridger-amplifiers 11 and 12 is (48,40), i.e. 48dBmV at 211.25 MHz and 40 dBmV at 55.25 MHz, the module A representingthe ZOO-foot cable 18 can then be positioned as already described on thechart 61 so that its top left-hand corner or reference position isdisposed at a point having those co-ordinates. Consequently, the lowerright-hand corner of the module will then be disposed at a point on thechart having co-ordinates corresponding to the signal strength level atthe input of the splitter 19. Then, by placing the module B with its topleft-hand corner at the same position as the bottom right-hand corner ofthe module A and with its sides parallel to the axes 64 and 65, thebottom righthand corner of the module B will be disposed at a point onthe chart 61 having coordinates corresponding to the signalstrengthlevel at the output 21 of that splitter. Similarly, bypositioning the remaining modules C through L on the chart 61 in serialdiagonal continuity as shown in FIG. 2, the signal strength levels atany position in the distribution line section 14 can readily be readfrom the chart.

The device 60 is shown in FIG. 2 as including an L- shaped guide 66including mutually perpendicular legs 67 and 68 which meet at an insideright angle corner 74. The guide 66 has openings therethrough so that itcan be secured in a desired fixed position on the chart 61 by thumbtacks 69 so that its inside corner 74 is positioned on the chart 61 insuch a way that it serves to locate the first module, for example,module A, of a series of such modules at a desired position as willreadily be understood byreference to FIG. 2. It should perhaps furtherbe explained that the guide 66 will also have utility in the device inaccordance with the invention as shown in FIG. 4 and yet to be describedherein. It is, however, equally within the scope of this invention toprovide a device in accordance therewith with other types of guides.

The operating characteristics of tap-offs, such as the tap-offs 24, 25,26, 27 and 28 used in the system shown in FIG. 1, are generallyexpressed by giving the signal strength attenuation between the inputand each of the tap-off outputs of such a component. For example, a 20dB two-way tap-off is one which gives a 20 dB attenuation of the inputsignal at each of the two reference frequencies between the input andeach of the two tapoff outputs. Referring further to FIG. 1, it will beseen that such characteristics for all the tap-offs shown therein areindicated parenthetically after the component legends on that figure.More particularly, it will be seen that each of the tap-offs 24 and 25gives a 20 dB attenuation while both the tap-offs 26 and 27 are rated at15 dB and the tap-off 28 is rated at 10 dB. The resulting tap-offsignal'strengths are also given on FIG. 1. It should perhaps be furtherexplained that the tapoffs used. in the distribution line section 14 ofthe system of FIG. 1 are selected so that the tap-off signal strengthlevels for the tap-offs 25, 27 and 28 are suitable for use with IOO-footdrop-line or lead-in cables while the tap-offs 24 and 26 are intendedfor use with ZOO-foot drop-line or lead-in cables. The aforementionedreferencesto the use of specific lengths of dropline or lead-in cablesare predicated on the use of the specific type of such cable presentlyavailable under the description RG-59. It should, however, beappreciated that the invention is equally applicable to distributionsystems using other types of cables. With the use of such other cabletypes, numerical signal strength values different from thosespecifically quoted herein will often apply.

Referring now to FIGS. 4' and 5 of the accompanying drawings, it will beseen that the alternative device in accordance with the invention asgenerally indicated at 75 in FIG. 4 has many features in common with thedevice 60 shown in FIG. 2. In particular, it will be noted that thedevice 75 includes a chart 76 which is almost identical with the chart61 of the device 60. The chart 76 differs from the chart 61 only in thatlines MIN. 13-100 and MIN. 13-200, and MIN. 2-100 and MIN. 2-200 areprovided on the chart parallel to the axes 65 and 64 respectivelythereof, suitably by printing. The reason these lines are provided willbe explained in greater detail as the description herein proceeds.

It will further be noted from FIG. 4 that thirteen modules M through Yare disposed on the chart 76 and that each of those modules has agenerally L-shaped configuration. The module M represents the 200-footcable 35 extending from the output of the bridger-amplifier 12 to theinput of the directional coupler 36 while the module N represents thedirectional coupler 36 itself. The module represents the ISO-foot cable44 while modules P, R, T and X represent the four-way tap-offs 39, 40,41 and 43 respectively while the module V represents the two-way tap-off42. The 100- foot lengths of cable 45, 46, 47 and 48 seriallyinterconnecting the tap-offs are represented by the modules 0, S, U andW respectively. The IOO-footcable 49 connecting the through output ofthe tap-off 43 to the distribution line amplifier 50 is represented bythe module Y.

Referring now to FIG. of the accompanying drawings, it will be seentherefrom that the module R representing the four-way tap-off 40 isshown enlarged in that figure. The module R includes a first leggenerally indicated at 78 and perpendicular thereto a second leggenerally indicated at 79. The first leg 78 of the module R has an outeror first side or dimension 80 which is coterminous with the outer orfirst side or dimension 81 of the leg 79 of the module at a first corneror reference position 82 of the module. The legs 78and 79 have innerside edges 83 and 84 respectively which meet at an inner corner 85. Theleg 78 has a width corresponding to the signal strength attenuation of1.2 dB at the Channel 2 picture carrier frequency between the input ofthe tap-off 40 and its through output at the same dimensional scale asthe scale 65 of the chart 76. Similarly, the leg 79 of the module R hasa width corresponding to the signal strength attenuation of 1.2 dB atthe Channell3 picture carrier frequency between the input of the tap-off40 and its through out put at the same dimensional scale as the scale 64of the chart 76. It will now be understood that the right quadrilateralportion of the moduleR common to both the legs 78 and 79 thereof can beutilized in the same manner as each of the modules A through I alreadydescribed herein is used while the extended legs 78 and 79 of thatmodule will serve to facilitate the correct mutual positioning ornesting of the modules on the chart 76. Insofar as modules representingcomponents which do not effect any division of their input signals areconcerned, the legs of the corresponding modules have no other purposeand such modules can be recognized in FIG. 4 as those having the outerends of their legs cut obliquely. For example, the module M servessimply to permit a graphical determination of the signal intensities atboth the Channels 2 and I3 picture carrier frequencies at the input tothe directional coupler 36.

In accordance with a particularly useful feature of this invention, themodules representing signal-dividing components as exemplified by thedirectional coupler 36 and the tap-offs 39, 40, 41, 42 and 43 are formedwith third and fourth dimensions corresponding to the attenuations ofthe input signal strengths at respective ones of the Channels 2 and 13picture carrier frequencies between the input of the component and theappropriate branch or tap-off output thereof. For example, the leg 78 ofthe module R shown in FIG. 5 is dimensioned so that the distance betweenthe outer edge 81 of the leg 79 and the outer end edge 86 of leg 78corresponds to the loss of signal strength at the Channel 13 picturecarrier frequency between the input of the tap-off 40 and each of thetap-off outputs of that component on the same dimensional scale as thescale 64 of the chart 76.

Similarly, the length of the leg 79 between the outer edge of the leg 78and the outer end edge 87 of the leg 79 will correspond to the signalstrength attenuation at the Channel 2 picture carrier frequency on thesame dimensional scale as the scale 65 of the chart 76 between the inputof the tap-off 40 and each of the tapoff outputs of that tap-off.

Although all'the tap-offs described herein are indicated as being oneswhich cause equal attenuation of signal strength at the two referencefrequencies on passage of a signal between the input and each of the tapoutputs of such a tap-off, it should be understood that the invention isequally applicable to tap-offs of the so-called sloped type and whichcause different signal strength attenuations at the two frequencies. Itwill further be understood that a tap-off with such a sloped"characteristic can be represented'by a module similar to module R buthaving legsof unequal lengths and generally of unequal widths.

It will now be understood that, by placing the module R on the chart 76with its first corner or reference position 82 at a point on that chartcorresponding to the input signal strengths at the input of the tap-off40, the through signal strengths to the cable 46 will be thosecorresponding to the position on that chart of the inner or secondcorner 85 of the module. Additionally, the signal strength levels at thetwo reference frequencies at each of the tap-off outputs can be readfrom the scales 64 and 65 of the chart as the positions along thosescales of the leg end edges 86 and 87 respective- Further utilization ofthis particular feature is illustrated in FIG. 4 in the case of themodule N representing the directional coupler 36. By comparing FIGS. 1and 4, it will be seen that the inner corner 88 of the module Nrepresents the signal strength level at the beginning of the cable 37while the signal strength level at the beginning of the cable 44 isrepresented by the point 89 on the chart, which point is located at theintersection of linear projections of the end edges 90 and 91 of thelegs of the module N.

It will now be understood that, by utilizing modules of the types shownin FIGS. 4 and 5, the present invention permits a rapid determination ofthe signal strength at any position in a distribution line of a cabletelevision signal distribution system including serially interconnectedcomponents as well as at branch and tap outputs of such a distributionline. This is particularly useful since, as previously indicated, it isgenerally necessary to optimize the signal strengths at such branch andtap outputs.

As previously indicated, the drop-line cables extending from the tap-offoutputs of a distribution line to subscribers receivers often havelengths of 100 or 200 feet and, in designing the distribution system, itis 'necessary for the designer to ensure that signal strengths withincertain predetermined ranges are made available to each and everysubscriber. With lower signal strength levels, receiver operation willfrequently be unsatisfactory due to the resulting low signalznoise ratiowhile, with too great a signal strength, distortion will frequentlyoccur. In accordance with yet a further feature of this invention, linesare provided on the chart 76, for example, by printing thereon, toindicate the minimum signal strengths which must be available at anytap-off output if the subscriber served by that output is to receiveadequate signal strength at his receiver for the length of drop-linecable actually to be used. Referring further to FIG. 4, it can beexplained that the line indicated MIN. 13-100 represents the minimumacceptable Channel 13 picture carrier frequency signal strength (I l.0dBmV) at a tap-off output where a l-foot drop-line will be used whilethe line identified MIN. 13-200 represents the minimum acceptableChannel 13 picture carrier frequency signal strength (l6.0 dBmV) at atap-off output where a 200- foot drop-line is to be used. Similarly, thelines identified MIN. 2-100 and MIN. 2-200 represent the minimumacceptable signal strengths at the Channel 2 picture carrier frequencyof 8.5 dBmV and l 1.0 dBmV for drop-lines having lengths of I00 and 200feet respectively.

The manner in which the device 75 is used in the designing of adistribution system will be better understood by further considering thecharacteristics of the tap-offs 39, 40, 41, 42 and 43 as represented bythe modules P, R, T, V and X respectively. The tap-off 39 shown is ofthe type giving a 20 dB loss at both the Channel 2 and Channel 13picture carrier frequencies between the input to the tap-off and each ofits outputs while both the tap-offs 40 and 41 give corresponding lossesof 15 dB and the tap-offs 42 and 43 are rated at dB. From FIG. 4, itwill be seen that the ends of the legs of the module R representing thetap-off 40 are disposed completely inwardly of both the lines MIN.

'2-200 and MIN. 13-200. Accordingly, adequate signal strength for a200-foot drop-line will be available from the tap-off 40. On the otherhand, the end of at least one of the legs of each of the modules P, T, Vand X representing the tap-offs 39, 41, 42 and 43 respectively isdisposed between the lines MIN. 2-200 and MIN. 2-100 and/or between thelines MIN. 13-200 and MIN. 13-100. Accordingly, adequate signalstrengths will be obtained from such tap-offs by the use of IOO-footdrop-lines but not by the use of 200-foot cables unless the Channel l3signal strength of 15.9 dBmV at each of the tap outputs of the tap-off42 is considered to be sufficiently close to the H50 dBmV value of theline MIN. 13-200 to permit the use of a 200-foot drop-line as acompromise. If tap-offs having the same characteristics as the tap-offs40 and 41 (Le. a 15 dB loss) were used instead of the tap-offs 42 and 43as'represented by the modules V and X respectively the ends of the legsof such modules would then be disposed outside both the lines MIN.13-100 and MIN. 2-100. As a result, the use of tap-offs with IS dB losscharacteristics would provide inadequate signal strength even withIOO-foot drop-lines for at least one frequency.

Using the device of FIG. 4, it is a very simple matter for a designer toposition modules representing the various available components on thechart 76 in nested disposition thereon as shown and then to determine byobservation of the modules whether adequate signal strengths will beavailable where required by the use of such components. In this way, theuse of the device greatly facilitates the designers selection ofsuitable components.

Referring further to the module X representing the tap-off 43, it willbe noted that the signal strength level available at thetap-off outputsof that component are sufficient provided that a l00-foot drop-line canbe used. If a 200-foot drop-line were required, it would then obviouslybe necessary to use a tap-off giving even less attenuation between itsinput and its tap-off outputs or to include a distribution lineamplifier in the distribution line before the tap-off 43.

Although the minimum signal strengths provided to individual subscribersare subject to statutory regulation in some countries, different valuesfor such minimum levels within the regulations but above the minimumvalues specified therein are adopted by different system operators. Forthis reason, it might be preferred not to provide the charts used in thedevice and method of this invention'with permanently printed lines suchas the lines MIN. 2-100, etc, as already described herein with referenceto FIG. 4 of the accompanying drawings. Furthermore, such minimum signalstrength lines can be provided in accordance with another useful featureof this invention on a transparent overlay which can be positioned overthe chart of a device before the various modules are disposed thereon.

Such a transparent overlay is indicated generally at 92 in FIG. 7 asbeing disposed over a chart 93 which is itself supported on a backingboard 94. The chart 93 is essentially identical to the chart 61 alreadydescribed herein but is provided with mounting holes (not shown) whichcan be aligned with corresponding mounting holes 95 provided in theoverlay 92 so as to receive thumb tacks 96 by means of which both thechart 93 and the overlay 92 can be secured to the board 94 in correctlyaligned positions thereon.

The overlay 92 has printed thereon four lines MIN. 2-100, MIN. 2-200,MIN. 13-100 and MIN. 13-200 corresponding to the lines provided on thechart 76 shown in FIG. 4. Additionally, lines (not shown) identifyingthe maximum signal strength levels which are generally considered asbeing acceptable for the corresponding lengths of drop-line cable can,if-desired, be provided on such an overlay. In accordance with yetanother feature of this invention, the overlay 92 is printed orotherwise marked with transparent bands 97, 98, 99, 100 and 101 whichare spaced apart from the lines MIN 2-100 and MIN. 13-100 topredetermined minimum distances. For example, the band 98 is defined bylower and right-hand edges 102 and 103 respectively which are spacedfrom respective ones of the aforementioned lines MIN. 2-100 and MIN.13-100 respectively by distances corresponding to signal strengthdifferences of 25 dB at each of the corresponding vtwo referencefrequencies. It will now be understood that, if a module representing atap-off or other signal-dividing component of the system and giving a 25dB loss of signal strength between its input and each of its tap orbranch outputs is positioned on the chart so that its first corner orreference position falls within the band 98, then it follows that asignal strength at each of the two reference frequencies greater thanthe minimum values represented by the lines MIN. 2-100 and MIN. 13-100will be available. For the particular overlay 92 shown in FIG. 7, theband 101 similarly corresponds to lOdB loss components while bands 100,99 and 97 correspond to component losses of 15, and 30 dB respectively.It has been found in practice that it is simpler, when using a deviceand method in accordance with the invention, to determine whether thereference corner or position of a module, such as the reference corner82 of the module R of FIG. 5, falls within a band such as the bandsshown in FIG. 7 than it is to inspect the legs of such a module todetermine the positions on the chart of the end edges of those legs asalready described herein with reference to FIG. 4.

It mustbe stressed, however, that the bands provided on the overlay 92shown in FIG. 7 will only apply when a lOO-foot drop-line can be used.If, for a particular subscriber, a ZOO-foot drop-line is required,reference would then need to be made to the positions on the chart ofthe end edges of the legs of the particular module relative to the linesMIN. 2-200 and MIN. 13-200. Similarly, the end edges of the legs of amodule are used to ensure that an excessive signal strength level is notprovided to any subscriber. Alternatively, such bands can be terminatedas at 104 and 105 for the band 100 for the same purpose.

The bands 97, 98, 99, 100 and 101 can, if desired, be of differentcolors so that they can be readily identified. Similarly, modulesrepresenting different types of system components or components withdifferent characteristics can also be color coded. On this matter,attention is again drawn to FIG. 4 from which it will be seen that themodules M, O, Q, S, U, W and Y representing cables are at leastpartially transparent to allow the underlying chart to be seen throughsuch modules while the modules N, P, R, T, V and X are essentiallyopaque. Such use of opaque modules to represent signal-dividingcomponents has been found to be advantageous in that it permits aphotograph of the chart with the modules positioned thereon to be takenso as to provide a permanent record of the system design, from whichrecord the various signal strength levels can easily be read at anytime.

In designing a cable television signal distribution system, it isconventional to utilize distribution line amplifiers which provide anoutput signal of a given fixed level at each of the two referencefrequencies. Reference will now be made to the alternative chart 106 inFIG. 6 of the accompanying drawings. On that chart, the standard outputsignal level from such a distribution lineamplifier is represented bythe point PS which is usefully provided, for example, by printing, onthe chart. The signal strength level at the input of a distribution lineamplifier will, however, generally need to be within a certain range soas to ensure that the desired operation of the amplifier can beobtained. When a variable gain/variable slope distribution lineamplifier is used, its permissible range of input signal strengths canbe represented on such a chart by a parallelogram, such as theparallelogram 107 on the alternative chart 106 shown in FIG. 6.

Provided that the input signal strength to the particular distributionline amplifier, corresponds to a point which is located within theparallelogram 107, that amplifier can then be adjusted to give an outputsignal having a signal strength at each of the two reference frequenciesas indicated by the point PS. On occasion, the signal intensities at agiven point in a distribution line are greater than those indicated bythe parallelo gram 107 but are so low that additional attenuatingcomponents such as tap-offs cannot be included in the line withoutfurther amplification. Similarly, it might be desired to incorporate anamplifier before a splitter to avoid the need for a greater number ofamplifiers in the output lines from such a splitter, In such situations,it is already known to utilize an amplifier with a signal-attenuatingadaptor so as to allow that amplifier to accept a higher strength inputsignal. Such adaptors are frequently referred to in the trade as pads orequalizers' and pads and/or equalizers with different operatingcharacteristics can be used in a single amplifier to give an evengreater range of acceptable input signal strengths. Such broader rangesfor the amplifier input signal strength are indicated in FIG. 6 by theparallelograms 108 and 109 printed on the chart 106 and representing theuse of twopads with different characteristics. Although thelast-mentioned chart shows the parallelograms 107, 108 and 109 as beingmutually overlapping, it will be understood that the chart could equallybe printed so that the overlapping portions of the parallelograms aredivided when the overlay is drawn so that a designer could then readilyidentify whether or not a pad or more than one pad should be used toobtain optimum amplifier performance.

It will be understood that the various modules used in this inventionwill normally be provided, for example, by printing ontheir topsurfaces, with indicia indicating the components which they respectivelyrepresent.

Although the invention has been described herein with particularreference to the specific embodiments thereof as illustrated in theseveral figures of the accompanying drawings, it should be understoodthat numerous modifications of the illustrated arrangements are possiblewithout departing from the scope of the inventive concept. Inparticular, it should be understood that the various optional featuresillustrated in the accompanying drawings can be utilized in the methodand device of the invention either separately or in variouscombinations, as desired and as appropriate. Other variations within thescope of the invention will readily be apparent to those conversant withthe relevant disciplines.

What is claimed is: l. A method for determining the values of twovariable parameters at a desired location within a distribution systemthroughout which said parameters have varying values and which methodcomprises the steps of:

disposing on a chart having mutually angularly oriented first and secondscales respectively representing values of said two parameters a modulerepresenting a preselected portion of said distribution system andhaving a first dimension corresponding to the change in the value of oneof said two parameters between input and output points ofsaidpreselected portion of said distribution system and a seconddimension corresponding to the change in the value of the other of saidtwo parameters between said input and output points of said preselectedportion of said distribution system, said first and second dimensions ofsaid module being coterminous at first ends thereof at a referenceposition and being mutually angularly oriented in correspondence withthe mutual angular orientation of said first and second scales of saidchart and said module being disposed on said chart with said referenceposition thereof at a position on said chart corresponding to the valuesof said two parameters at said input point of said preselected portionof said distribution system and with said first and second dimensions ofsaid module disposed parallel to respective ones of said first andsecond scales of said chart; identifying a read-out position on saidchart corresponding to an outer end of a resultant of said first andsecond dimensions of said module; and

reading from said first and second scales ofsaid chart values ofrespective ones of said two parameters corresponding to said outer endof said resultant of said first and second dimensions of said module,thereby to give the values of said two parameters at said output pointof said preselected portion of said distribution system.

2. A method as claimed in claim 1 for determining the-values of said twoparameters at each of first and second output points of said preselectedportion of said distribution system and in which said first and seconddimensions of said module correspond to the changes in the values ofrespective ones of said first and second parameters between said inputpoint and said first output point of said preselected portion of saiddistribution system, said module further having third and fourthdimensions corresponding to the changes in the values of respective onesof said two parameters between said input point and said second outputpoint of said preselected portion of said distribution system and saidthird and fourth dimensions of said module being coterminous at firstends thereof at said reference position, being mutually angularlyoriented in correspondence with the mutual angular orientation of saidfirst and second scales of said chart and being disposed parallel torespective ones of said first and second scales of said chart, and whichmethod additionally comprises identifying a second readout position onsaid chart, said second read-out position corresponding to an outer endof a resultant of said third and fourth dimensions of said module andreading from said first and second scales of said chart' values ofrespective ones of said two parameters corresponding to the said outerend of said resultant of said third and fourth dimensions of said modulethereby additionally to give the values of said two parameters at saidsecond output point of said preselected portion of said distributionsystem.

3. A method as claimed in claim 2 for determining the values of signalintensity at two different frequencies at said first and second outputpoints of a signal divider included in a radio frequency signal cabledistribution system and which method comprises disposing on said charton which said two scales are provided essentially perpendicularly toeach other, said module having said first and third dimensions, on theone hand, said and said second and fourth dimensions, on the other hand,essentially perpendicular to each other, said first and seconddimensions of said module corresponding to the changes in values ofsignal intensity at respective ones of said two frequencies between saidinput point and said first output point of said signal divider and saidthird and fourth dimensions of said module corresponding to the changesin the values of signal intensity at respective ones of said twofrequencies between said input point and said second output point ofsaid signal divider.

4. A method as claimed in claim 3 which comprises disposing a pluralityof said modules on said chart in mutually nested disposition and indiagonal serial continuity thereon. i

5. A method as claimed in claim 4 which comprises the additional step ofpreparing a photographic record of said modules disposed on said chart.

6. A method as claimed in claim 1 which comprises serially disposing aplurality of said modules on said chart and reading therefrom respectivevalues of said two parameters at output points of a correspondingplurality of preselected portions of said distribution system.

7. A method as claimed in claim 6 in which an initial one of saidmodules is disposed on said chart with said reference position thereofdisposed on said chart at a position identified thereon andrepresentative of the values of said two parameters at the output pointof-a preselected component of said distribution system.

8. A method as claimed in claim 1 for determining the values ofrespective signal intensities at two different frequencies at apreselected location in a radio frequency signal cable distributionsystem and which method comprises disposing on said chart on which saidtwo scales are provided essentially perpendicularly to each other saidmodule having said first and second dimensions thereof essentiallyperpendicular to each other, said first and second dimensions of saidmodule corresponding to the changes in values of signal intensity atrespective ones of said two frequencies between said input and outputpoints of said preselected portion of said distribution system.

9. A method as claimed in claim 8 in which said first and seconddimensions of said module represent the losses in the values of signalintensity at respective ones of said two different frequencies onpassage of radio frequency signals between input and output ends of apreselected length of distribution cable forming part of saiddistribution system.

10. A device for determining the values of two variable parameters at adesired location within a distribution system throughout which saidparameters have varying values and which device comprises:

a chart having thereon mutually angularly oriented first and secondscales respectively representing values of said two parameters, and

a module representing a preselected portion of said distribution systemand having a first dimension corresponding to the change in value of oneof said two parameters between input and output points of saidpreselected portion of said distribution system and a second dimensioncorresponding to the change in value of the other of said two parametersbetween said input point and said output point of said preselectedportion of said distribution system, said first and second dimensions ofsaid module being coterminous at first ends thereof at a referenceposition and being mutually angularly oriented in correspondence withthe mutual angular orientation of said first and second scales of saidchart,

whereby, when said module is disposed on said chart with said referenceposition of said module at a position on said chart corresponding to thevalues of said two parameters at said input point of said preselectedportion of said distribution system and with said first and seconddimensions of said module disposed parallel to respective ones of saidfirst and second scales of said chart, a read-out position can beidentified on said chart by locating the outer end of a resultant ofsaid first and second dimensions of said module in turn to allow valuesof respective ones of said two parameters to be read from respectiveones of said first and second scales of said chart, theresultingreadings being indicative of the values of-respective ones of said twoparameters at said output point of said preselected portion of saiddistribution system.

11. A device as claimed in claim 10 in which said first and secondscales of said chart are disposed essentially perpendicularly to eachother and in which said first and second dimensions of said module areconstituted by respective ones of mutually perpendicular first andsecond side edges of said module which side edges are coterminous at afirst corner of said module, said first corner constituting saidreference position, and in which said module has a right quadrilateralportion with a second corner thereof disposed diagonally relative tosaid first corner whereby said values of said two parameters at saidoutput point can be read from respective ones of said first and secondscales of said chart at the positions therealong of said second cornerof said module when said first corner of said module is disposed on saidchart at a position thereon corresponding to the values of respectiveones of said two parameters at said input point of said preselectedportion of said distribution system.

12. A device as claimed in claim 11 in which said first and secondscales of said chart are logarithmic representations of the variationsof the signal intensities at two different frequencies in a radiofrequency signal cable distribution system and in which said first andsecond dimensions of said module represent changes in the values ofsignal intensity at respective ones of said two different frequenciesthrough a preselected portion of said distribution system.

13. A device as claimed in claim 12 including a plurality of saidmodules whereby said modules can be disposed on said chart in diagonalserial continuity whereby in turn values of said signal intensities canbe determined at output points of a corresponding plurality ofpreselected portions of said distribution system.

14. A device as claimed in claim 11 in which said module has mutuallyperpendicular legs extending from said right quadrilateral portionthereof with outer edges of said legs forming linear extensions ofrespective ones of said first and second side edges of said rightquadrilateral portion of said module and with inner edges of said legscoterminous at said second corner of said module.

15. A device as claimed in claim 14 in which said legs of said modulehave lengths corresponding to changes in the values of respective onesof said two parameters between said input point and a second outputpoint of said preselected portion of said distribution system.

16. A device as claimed in claim 15 in which at least some of saidmodules are formed of a transparent material.

17. A device as claimed in claim 16 in which each said modulerepresenting a preselected portion of said distribution system having asaid second output point is formed of an essentially opaque materialwhile each said module representing a preselected portion of saiddistribution system having only a said first output point is formed ofan essentially transparent material.

18. A device as claimed in claim 15 in which said first and secondscales of said chart are logarithmic representations of the variationsof the signal, intensities at two different frequencies in a radiofrequency signal cable distribution system, in which said first andsecond dimensions of said module represent changes in the values ofsignal intensity at respective ones of said two different frequenciesbetween an input point and a first output point of said preselectedportion of said distribution system, and in which said lengths of saidlegs represent changes in the values of signal intensity at respectiveones of said two different frequencies between an input point and asecond output point of said preselected portion of said distributionsystem.

19. A device as claimed in claim 18 including a plurality of saidmodules whereby said modules can be disposed on said chart in seriallynested positions thereon.

20. A device as claimed in claim 19 in which said chart has apredetermined minimum signal intensity level provided thereon for atleast one of said two frequencies.

21. A device as claimed in claim 19 in which said chart has providedthereon at least one zone representative of the overall permissibleinput range of a preselected, variable slope, variable gain signalamplifi- 22. A device as claimed in claim 19 and which deviceadditionally includes a transparent overlay for said chart, said overlayhaving recorded thereon a predetermined minimum signal intensity levelfor at least one of said two frequencies.

23. A device as claimed in claim 22 in which said transparent overlayhas recorded thereon at least one band corresponding to a predeterminedrange of signal intensities at each of said two frequencies such that,when-a preselected said module is disposed on said overlay with saidreference position of said module within said band, the values of signalintensity at each of said two frequencies at said second output point ofsaid preselected portion of said distribution system are at least equalto predetermined values thereof.

24. A module for use in designing a radio frequency signal cabledistribution system, which module includes a generally planarundersurface and a top surface and which module has indicia visiblyrecorded thereon to designate a corresponding signal-modifying componentof a radio frequency signal cable distribution system, said modulehaving mutually angularly oriented first and second side edgescoterminous at a first corner of said module, said first side edge ofsaid module having at least a section thereof with a lengthcorresponding to the change in signal intensity at a first frequency onpassage of a radio frequency signal through the corresponding componentbetween an input and an output thereof, said second side edge of saidmodule having at least a section thereof with a length corresponding tothe change in signal intensity at a second frequency on passage of aradio frequency signal through the corresponding component between theinput and the output thereof, and said module having a second cornerdisposed at an outer end of a resultant of said sections of said firstand second side edges of said module.

25. A module as claimed in claim 24 in which said module is a generallyplanar member with said indicia visibly recorded on said top surfacethereof and having a generally L-shaped configuration including twomutually perpendicular legs defined by respective pairs of mutuallyparallel inner and outer edges, said outer edges of said legs beingcoterminous at said first corner of said module, said inner edges ofsaid legs being coterminous at said second corner of said module, saidinner and outer edges of each said leg of said module being mutuallyspaced apart a distance corresponding to the change in signalintensityat a respective one of said first and second frequencies on passage of aradio frequency signal through the corresponding component between theinput and the output thereof.

26. A module as claimed in claim 25' in which each said leg thereof hasa length corresponding to the change in signal intensity at a respectiveone of said first and second frequencies on passage of a radio frequencysignal through the corresponding component between the input and asecond output of that component.

1. A method for determining the values of two variable parameters at adesired location within a distribution system throughout which saidparameters have varying values and which method comprises the steps of:disposing on a chart having mutually angularly oriented first and secondscales respectively representing values of said two parameters a modulerepresenting a preselected portion of said distribution system andhaving a first dimension corresponding to the change in the value of oneof said two parameters between input and output points of saidpreselected portion of said distribution system and a second dimensioncorresponding to the change in the value of the other of said twoparameters between said input and output points of said preselectedportion of said distribution system, said first and second dimensions ofsaid module being coterminous at first ends thereof at a referenceposition and being mutually angularly oriented in correspondence withthe mutual angular orientation of said first and second scales of saidchArt and said module being disposed on said chart with said referenceposition thereof at a position on said chart corresponding to the valuesof said two parameters at said input point of said preselected portionof said distribution system and with said first and second dimensions ofsaid module disposed parallel to respective ones of said first andsecond scales of said chart; identifying a read-out position on saidchart corresponding to an outer end of a resultant of said first andsecond dimensions of said module; and reading from said first and secondscales of said chart values of respective ones of said two parameterscorresponding to said outer end of said resultant of said first andsecond dimensions of said module, thereby to give the values of said twoparameters at said output point of said preselected portion of saiddistribution system.
 2. A method as claimed in claim 1 for determiningthe values of said two parameters at each of first and second outputpoints of said preselected portion of said distribution system and inwhich said first and second dimensions of said module correspond to thechanges in the values of respective ones of said first and secondparameters between said input point and said first output point of saidpreselected portion of said distribution system, said module furtherhaving third and fourth dimensions corresponding to the changes in thevalues of respective ones of said two parameters between said inputpoint and said second output point of said preselected portion of saiddistribution system and said third and fourth dimensions of said modulebeing coterminous at first ends thereof at said reference position,being mutually angularly oriented in correspondence with the mutualangular orientation of said first and second scales of said chart andbeing disposed parallel to respective ones of said first and secondscales of said chart, and which method additionally comprisesidentifying a second readout position on said chart, said secondread-out position corresponding to an outer end of a resultant of saidthird and fourth dimensions of said module and reading from said firstand second scales of said chart values of respective ones of said twoparameters corresponding to the said outer end of said resultant of saidthird and fourth dimensions of said module thereby additionally to givethe values of said two parameters at said second output point of saidpreselected portion of said distribution system.
 3. A method as claimedin claim 2 for determining the values of signal intensity at twodifferent frequencies at said first and second output points of a signaldivider included in a radio frequency signal cable distribution systemand which method comprises disposing on said chart on which said twoscales are provided essentially perpendicularly to each other, saidmodule having said first and third dimensions, on the one hand, said andsaid second and fourth dimensions, on the other hand, essentiallyperpendicular to each other, said first and second dimensions of saidmodule corresponding to the changes in values of signal intensity atrespective ones of said two frequencies between said input point andsaid first output point of said signal divider and said third and fourthdimensions of said module corresponding to the changes in the values ofsignal intensity at respective ones of said two frequencies between saidinput point and said second output point of said signal divider.
 4. Amethod as claimed in claim 3 which comprises disposing a plurality ofsaid modules on said chart in mutually nested disposition and indiagonal serial continuity thereon.
 5. A method as claimed in claim 4which comprises the additional step of preparing a photographic recordof said modules disposed on said chart.
 6. A method as claimed in claim1 which comprises serially disposing a plurality of said modules on saidchart and reading therefrom respective values of said two parameters atoutput points of a corresponding pluRality of preselected portions ofsaid distribution system.
 7. A method as claimed in claim 6 in which aninitial one of said modules is disposed on said chart with saidreference position thereof disposed on said chart at a positionidentified thereon and representative of the values of said twoparameters at the output point of a preselected component of saiddistribution system.
 8. A method as claimed in claim 1 for determiningthe values of respective signal intensities at two different frequenciesat a preselected location in a radio frequency signal cable distributionsystem and which method comprises disposing on said chart on which saidtwo scales are provided essentially perpendicularly to each other saidmodule having said first and second dimensions thereof essentiallyperpendicular to each other, said first and second dimensions of saidmodule corresponding to the changes in values of signal intensity atrespective ones of said two frequencies between said input and outputpoints of said preselected portion of said distribution system.
 9. Amethod as claimed in claim 8 in which said first and second dimensionsof said module represent the losses in the values of signal intensity atrespective ones of said two different frequencies on passage of radiofrequency signals between input and output ends of a preselected lengthof distribution cable forming part of said distribution system.
 10. Adevice for determining the values of two variable parameters at adesired location within a distribution system throughout which saidparameters have varying values and which device comprises: a charthaving thereon mutually angularly oriented first and second scalesrespectively representing values of said two parameters, and a modulerepresenting a preselected portion of said distribution system andhaving a first dimension corresponding to the change in value of one ofsaid two parameters between input and output points of said preselectedportion of said distribution system and a second dimension correspondingto the change in value of the other of said two parameters between saidinput point and said output point of said preselected portion of saiddistribution system, said first and second dimensions of said modulebeing coterminous at first ends thereof at a reference position andbeing mutually angularly oriented in correspondence with the mutualangular orientation of said first and second scales of said chart,whereby, when said module is disposed on said chart with said referenceposition of said module at a position on said chart corresponding to thevalues of said two parameters at said input point of said preselectedportion of said distribution system and with said first and seconddimensions of said module disposed parallel to respective ones of saidfirst and second scales of said chart, a read-out position can beidentified on said chart by locating the outer end of a resultant ofsaid first and second dimensions of said module in turn to allow valuesof respective ones of said two parameters to be read from respectiveones of said first and second scales of said chart, the resultingreadings being indicative of the values of respective ones of said twoparameters at said output point of said preselected portion of saiddistribution system.
 11. A device as claimed in claim 10 in which saidfirst and second scales of said chart are disposed essentiallyperpendicularly to each other and in which said first and seconddimensions of said module are constituted by respective ones of mutuallyperpendicular first and second side edges of said module which sideedges are coterminous at a first corner of said module, said firstcorner constituting said reference position, and in which said modulehas a right quadrilateral portion with a second corner thereof disposeddiagonally relative to said first corner whereby said values of said twoparameters at said output point can be read from respective ones of saidfirst and second scales of said charT at the positions therealong ofsaid second corner of said module when said first corner of said moduleis disposed on said chart at a position thereon corresponding to thevalues of respective ones of said two parameters at said input point ofsaid preselected portion of said distribution system.
 12. A device asclaimed in claim 11 in which said first and second scales of said chartare logarithmic representations of the variations of the signalintensities at two different frequencies in a radio frequency signalcable distribution system and in which said first and second dimensionsof said module represent changes in the values of signal intensity atrespective ones of said two different frequencies through a preselectedportion of said distribution system.
 13. A device as claimed in claim 12including a plurality of said modules whereby said modules can bedisposed on said chart in diagonal serial continuity whereby in turnvalues of said signal intensities can be determined at output points ofa corresponding plurality of preselected portions of said distributionsystem.
 14. A device as claimed in claim 11 in which said module hasmutually perpendicular legs extending from said right quadrilateralportion thereof with outer edges of said legs forming linear extensionsof respective ones of said first and second side edges of said rightquadrilateral portion of said module and with inner edges of said legscoterminous at said second corner of said module.
 15. A device asclaimed in claim 14 in which said legs of said module have lengthscorresponding to changes in the values of respective ones of said twoparameters between said input point and a second output point of saidpreselected portion of said distribution system.
 16. A device as claimedin claim 15 in which at least some of said modules are formed of atransparent material.
 17. A device as claimed in claim 16 in which eachsaid module representing a preselected portion of said distributionsystem having a said second output point is formed of an essentiallyopaque material while each said module representing a preselectedportion of said distribution system having only a said first outputpoint is formed of an essentially transparent material.
 18. A device asclaimed in claim 15 in which said first and second scales of said chartare logarithmic representations of the variations of the signalintensities at two different frequencies in a radio frequency signalcable distribution system, in which said first and second dimensions ofsaid module represent changes in the values of signal intensity atrespective ones of said two different frequencies between an input pointand a first output point of said preselected portion of saiddistribution system, and in which said lengths of said legs representchanges in the values of signal intensity at respective ones of said twodifferent frequencies between an input point and a second output pointof said preselected portion of said distribution system.
 19. A device asclaimed in claim 18 including a plurality of said modules whereby saidmodules can be disposed on said chart in serially nested positionsthereon.
 20. A device as claimed in claim 19 in which said chart has apredetermined minimum signal intensity level provided thereon for atleast one of said two frequencies.
 21. A device as claimed in claim 19in which said chart has provided thereon at least one zonerepresentative of the overall permissible input range of a preselected,variable slope, variable gain signal amplifier.
 22. A device as claimedin claim 19 and which device additionally includes a transparent overlayfor said chart, said overlay having recorded thereon a predeterminedminimum signal intensity level for at least one of said two frequencies.23. A device as claimed in claim 22 in which said transparent overlayhas recorded thereon at least one band corresponding to a predeterminedrange of signal intensities at each of said two frequencies such that,when A preselected said module is disposed on said overlay with saidreference position of said module within said band, the values of signalintensity at each of said two frequencies at said second output point ofsaid preselected portion of said distribution system are at least equalto predetermined values thereof.
 24. A module for use in designing aradio frequency signal cable distribution system, which module includesa generally planar undersurface and a top surface and which module hasindicia visibly recorded thereon to designate a correspondingsignal-modifying component of a radio frequency signal cabledistribution system, said module having mutually angularly orientedfirst and second side edges coterminous at a first corner of saidmodule, said first side edge of said module having at least a sectionthereof with a length corresponding to the change in signal intensity ata first frequency on passage of a radio frequency signal through thecorresponding component between an input and an output thereof, saidsecond side edge of said module having at least a section thereof with alength corresponding to the change in signal intensity at a secondfrequency on passage of a radio frequency signal through thecorresponding component between the input and the output thereof, andsaid module having a second corner disposed at an outer end of aresultant of said sections of said first and second side edges of saidmodule.
 25. A module as claimed in claim 24 in which said module is agenerally planar member with said indicia visibly recorded on said topsurface thereof and having a generally L-shaped configuration includingtwo mutually perpendicular legs defined by respective pairs of mutuallyparallel inner and outer edges, said outer edges of said legs beingcoterminous at said first corner of said module, said inner edges ofsaid legs being coterminous at said second corner of said module, saidinner and outer edges of each said leg of said module being mutuallyspaced apart a distance corresponding to the change in signal intensityat a respective one of said first and second frequencies on passage of aradio frequency signal through the corresponding component between theinput and the output thereof.
 26. A module as claimed in claim 25 inwhich each said leg thereof has a length corresponding to the change insignal intensity at a respective one of said first and secondfrequencies on passage of a radio frequency signal through thecorresponding component between the input and a second output of thatcomponent.